Function Blocks UM353-1
March 2003
3-12
G
r
= real gas relative density (specific gravity)
Z
s
= compressibility at standard conditions
Z
f
= compressibility at flowing conditions at upstream tap - Z
f1
Z
b
= compressibility at base conditions
The specific gravity factor (
G
r
) and the compressibility factors (
Z
s
, Z
f
, Z
b
) can be entered manually using HLD
(Hold) function blocks, computed, and then downloaded from a host device, or calculated in the controller using the
AG8 (AGA 8 Compressibility Factors of Natural Gas) function block.
The following are analog outputs of the AGA 3 function block:
Q
b
= volume flow rate at base conditions (SCFH - Standard Cubic Feet per Hour)
C' = composite orifice flow factor [SCFH/
√
(psia)(in H2O)]
h
w
P
f
T
f
G
r,
Z
f,s,b
Q
b
AGA 3
Application Diagram
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